The dummy block construction as described in applicant's U.S. Pat. Nos. 5,272,900 and 5,311,761 provide a venting device for the dummy block and a bayonet type connector for connecting the dummy block to a stem of an extrusion press. The venting device which is more commonly referred to as a plunger is pushed inwardly of the dummy block when the dummy block abuts a billet of extrudable metal in a container of an extrusion press. When the venting device is closed it expands slightly the dummy block circumference to contact the interior surface of the container to preclude thereby metal flashing beyond and behind the dummy block face. With correct machining of the dummy periphery and positioning of the plunger, the dummy block periphery can be expanded to the extent desired to minimize metal flashing. However, over extended periods of use, the circumferential portion of the dummy block looses its strength and hence fails to seal the face of the dummy block to the container interior, hence metal flashing becomes a problem. Also, as the circumferential portion of the dummy block looses its strength, the plunger may wedge and become jammed within the dummy block, so that it does not release when the dummy block is retracted from the container of the extrusion press. It is then necessary to return the dummy block for refurbishing and retooling whereby the refurbished dummy block has a circumferential forward portion which exhibits the desired strength characteristics to minimize flashing and minimize jamming of the plunger within the dummy block.
Although the above type of dummy block construction is particularly suited to the extrusion of various extrudable metals which include aluminium alloy, copper, bronze, brass and the like, various attempts have been to solve the problem associated with the above type of dummy block. Various types of wear rings have been provided on the dummy block, for example, U.S. Pat. No. 4,024,743 describes a compressible, expandable seal for use in a piston extrusion of hot or cold metal billet. The seal is designed to flow outwardly of the plunger and contact is the container to prevent flashing of metal beyond and behind the plunger. This system normally hangs up on the butt portion of the billet in the container, so that when the plunger is withdrawn, the seal is destroyed which requires replacement. A bolt may be used as it extends through the dummy block components to squeeze the seal between the dummy block components.
U.S. Pat. No. 3,977,226 describes a floating ring seal for extruding metals. The floating ring seal has the same problem as the seal in U.S. Pat. No. 4,024,743. When the ram is withdrawn from the container, the seal will hang up on the butt of the billet of extruded metal, requiring clean out of the extrusion container.
U.S. Pat. No. 3,831,418 describes a dye assembly for extruding aluminium and its alloys. The dye assembly includes a ring at the face of the dye assembly and which is expanded outwardly by inwardly sloping surfaces converging towards the front of the dye assembly. This requires that the ring move rearwardly of the edge assembly in order to expand and engage container wall thereby exposing a portion of the front of the dye assembly. Due to this movement of the ring in the reverse direction along the dye assembly, gaps may be created through which metal may flash beyond and behind the dye assembly. This causes significant problems with respect to removal of the dye assembly from the extrusion container. With either the interlocking engaging teeth or bayonet style connection of the ring to the dye assembly, the ring in moving rearwardly does not expand readily because of the low surface area of the ring which has exposed the metal billet and hence further metal flashing may be a problem around the perimeter of the dye assembly.
Russian Patent 569,354 describes a dummy block system for metal extruders which has a conical ring with a conical outside surface for expanding the ring as the dummy block contacts the billet of material in the extruder container. The ring is thin and is caused to expand by sliding rearwardly on a sloping face of the dummy block. A forward portion of the dummy block is slidably mounted to move rearwardly and push the ring up the sloped surface. The face of the dummy block has a indentation where the metal portion which moves the ring rearwardly has to advance onto the dummy block structure.
This as well can cause significant metal flashing problems where the pressures within the container can exceed upwardly of 100,000 psi. Any clearance at all will result immediately in metal flashing and thereby block the extraction of the dummy block from the extruder container. Furthermore, with the relative slope of the ring to the dummy block surfaces, there is a greater likelihood of jamming because the angle of the sloping surfaces is considerably less than 20.degree. from the longitudinal axis of the dummy block. This can also result in the ring jamming and staying expanded and thereby further hindering the extraction or withdrawal of the dummy block from the extruder container.
German Patent Application 4,132,810 describes a dummy block construction for a metal extruder where the seal arrangement is like that described in U.S. Pat. No. 4,024,743. The dummy block has a central piston with a convex shaped face. The piston is moved rearwardly into the dummy block to expand the seal and engage thereby the container interior surface. The seal has a tendency to hang up on the interior of the container at the completion of an extrusion cycle. Furthermore, the piston can yield which would inherently reduce the extent of expansion of the seal and thereby result in a significant problem regarding metal flashing passing beyond and behind the dummy block.
Other systems for expanding the dummy block perimeter to engage the extrusion container interior wall are described in U.S. Pat. Nos. 3,919,873 and 4,550,584. As already discussed the problem with the system of U.S. Pat. No. 4,550,584 is that the metal of the dummy block body portion fatigues, requiring replacement of the entire block body portion. As to the system of U.S. Pat. No. 3,919,873, a convex indentation is provided in the face of the dummy block to encourage expansion of the dummy block. In the alternative the telescoping of a disk within the dummy block face can be relied on to expand the dummy block. A bolt is used to hold the disk to the face of the dummy block where resilient devices bias the disk to the outward position.
In applicant's aforementioned U.S. Pat. No. 5,272,900, the system is set up to position the spring between the bayonet connector post and the end of the plunger post. This arrangement facilitates access to the rear of the plunger so that the plunger could be removed from the dummy block and also biased the bayonet connector to study it for purposes of assembly to the extruder stem. This arrangement involves a number of component parts which involve extra machine time and in particular involves expensive threading within the dummy block per se.
Accordingly, this invention overcomes a number of the above problems by providing an improved wear ring on the dummy block which is substantial in form and constitutes a replaceable collar about the forward portion of the dummy block. An improved design with respect to a plunger which enters the dummy block during the extrusion process ensures a consistent reproducible expansion of the collar to seal the container interior and thereby minimize metal flashing beyond and behind the dummy block and as well minimize jamming of the plunger within the dummy block by virtue of the expanded collar.